In a multiplicity of examinations of patients using advanced examination and diagnostic devices, for example magnetic resonance scanners, it is useful or even essential to monitor and/or record a patient's vital functions, e.g. his/her breathing and heartbeat, during the examination.
This may be necessary on the one hand for monitoring the patient's condition, in particular if the patient has been sedated or anesthetized. On the other hand it is necessary in many modern-day examination procedures to synchronize an acquisition of data included as part of the examination with a movement caused by the patient's vital functions. In particular in the case of magnetic resonance examinations a synchronization of said type is frequently used in order to minimize motion artifacts in acquired images and/or in order to enable an image to be acquired at a desired time instant during the movement, e.g. respiratory movement or heartbeat.
Monitoring the vital functions is not, however, possible simply as a matter of course if the patient is situated inside the examination and diagnostic device during the examination so that he/she cannot be observed from outside.
For this purpose it is known for example to measure ECG signals by means of an ECG measuring instrument and use them for generating trigger signals for the data acquisition during the examination (ECG: electrocardiogram). During the imaging information about the cardiac phase is obtained by way of the ECG signal so that the imaging can be synchronized with the activity of the heart. ECG measuring instruments are also used during an examination of a patient by means of a magnetic resonance device for in-situ recording of ECG signals. In this case, however, due to the strong gradient fields and high-frequency fields used for imaging in a magnetic resonance device, operation therein imposes special demands on the ECG measuring instrument in order to prevent mutual interference between magnetic resonance device and ECG measuring instrument. ECG measuring instruments which are magnetic resonance compatible within the above-cited meaning are commercially available. However, determining so-called “R waves” in the recorded ECG signals, which is essential for reliable triggering, is still not reliably possible e.g. due to interference voltages that are generated by electromagnetic alternating fields and coupled as noise into the ECG signal acquired by the ECG electrodes and overlay the actual ECG signal.
In order to register respiratory movements it is known to use so-called “respiratory belts” which are strapped around the patient's torso and transmit a compression of the pneumatically operating respiratory belt caused by the respiratory movement via a tubing system to a recording device located outside of the medical examination and diagnostic device. However, the accuracy of the thus detected respiratory movement is not always sufficient for reliable monitoring or for triggering data acquisitions.
Alternatively it is known in MR examinations (MR: Magnetic Resonance) to determine the respiratory movements of a patient by means of so-called “navigator measurements” which are performed in addition to the actual MR measurement. However, this requires intricate planning of the measurements and increases the overall exposure of the patient to irradiated energy.
The publication by Henneberg S. et al: “Remote auscultatory patient monitoring during magnetic resonance imaging”, J Clin Monit 1992, 8:37-43, discloses a stethoscope having an acoustic signaling line for monitoring the respiratory sounds and heart sounds of sedated or anesthetized patients during an MR examination.
A stethoscope that has an acoustic signaling line and is used for triggering MR scans is known from the publication by Frauenrath Tobias et al: “The MR stethoscope: safe cardiac gating free of interference with electro-magnetic fields at 1.5 T, 3.0 T and 7.0 T”, Journal of Cardiovascular Magnetic Resonance 2009, 11(Suppl 1), pp. 63-64.
An acoustic signaling line is subject to strong attenuation effects, with the result that the quality of the transmitted signals deteriorates rapidly as the length of the signaling line increases.